This invention relates to a cushion material with use of conjugated fibers and a method for the preparation thereof.
Various cushion materials made of polyester fibers have been developed. They are usually prepared by using two types of polyester fibers having different melting points with respect to each other or using core-sheath type conjugated fibers, and heat-treating in a hot air circulating oven to melt the component having a low melting point. However, in this procedure, the hot air is passed through the interior of the webs in the case of a relatively low density not higher than 0.01 g/cm.sup.2 and hence unevenness in density occurs to the direction of thickness of the cushion material due to air pressure. On the other hand, in the preparation of a high density cushion material, the hot air is difficult to pass it through so that the thickness of it is restricted. Furthermore, since the heating mechanism is mainly convection and conduction, the loss in energy is disadvantageously high. In Japanese Laid-Open Patent Publication No. 223,357 of 1987, there has been proposed a method for the preparation of a cushion material by using far-infrared ray as the heat source to overcome such disadvantages. In its Examples, a use of core-sheath type conjugated fibers having sheath of a low melting substance is disclosed.
The heating mechanism of this method is radiation and the energy in the long wave region of far-infrared ray is absorbed in the fiber material and causes internal heating by molecular vibration and thus the heat-fusable fibers in the webs are efficiently molten. Hence, it causes no unevenness in density caused by air pressure as seen in the hot air circulating oven and also the process can be carried out at low temperature in a short period to give good workability. However, it has a disadvantage of that, when the web is thick, it is difficult to melt the interior.
Furthermore, Japanese Laid-Open Patent Publication No. 811, 050 of 1983 discloses a product in which the interconnections are fused by melting low-melting fibers with steaming. In this case, the interconnections can be fixed by melting the low-melting fibers without adhesives and resultantly a product having a good cushioning property can be obtained in a relatively stable condition, but it has problems in workability.
Thus, the methods of heat treatment for the preparation of the cushion material have both merits and demerits and they cannot provide voluminous products having no strain by compression set.
The object of the present invention is to provide a voluminous cushion material consisting of polyester fibers, which has a high quality and little strain by compression set so that it can be used as a mat for bed, and a method for the preparation thereof.
The inventors have found that the above object can be attained by using specific conjugated fibers and combining the advantages of far-infrared ray or hot air flow heating and steaming in heating.